Variable electric chokes, transformers, or the like



y 1952 H. MULLER 2,602,097

' VARIABLE ELECTRIC CHOKES, TRANSFORMERS OR THE LIKE Filed Jan. 8, 1949 2 SHEETSSHEET 1 HEMP/cw M04452 H. MULLER July 1, 1952' VARIABLE ELECTRIC CHOKES, TRANSFORMERS OR THE LIKE 2 SHEETS-SHEET 2 Filed Jan. 8, 1949 'whethernsed for 01" with D. C.

said "required maximum amperage.

amperage and/ or fluii is required. l On: the I other hand; a devicahavingza' re Patented July 1, 1952 UNITED sk'mriss VARIABLE EL PATENT iiGfFiF-ICE ECTRIC'YCH'OKESLTRA'NS- 'FORMER'S, ORiTHE' LIKE Heinrich Muller; Manchesterg England Applicationlanuary s, 1'949',Serial No." 69,861: if'In Great Britain January '10; 1948 This invention'relates to variable electric magn'etic devices such as inductances, -chokes,' tr'ans- -formers or the like for-A. C. or relaysgsolenoids etcxforA. Caor D. (Ly-of the kind havinga shellshaped magnetic -core, that is --to 1 say havinga 'core'which in its'simplest form may be described as consisting of a closed outer frame across which is'a centrelimb. Various cores are alsoknown, "for eXamp-le-f'orfinulti-phase-use, which are cornpounded forms-"ohaplurality of simple shellshapedcores and as-"such are included in -the expression shell-shaped core as used herein single ornnilti-iahase purposes One or the objects *of a designer of "a' va'riable electio-magnetit: device is to obtain for a given amountof copper and iron, a maximum control range of current and/or flux vanaem- An0ther object-is to make the variation-within such range infinitely variable and this latter obj ect as' is of course welbknown, is more easily obtainable by providing relative physical movement of the copperand iron"rather than by-"the use or tappings. The-possible range of variation'is'deterrnined by certain factors. 'For example; the minimum copper section of the=-condutor is'determined by themaximum 1 required amperage, *and if there is to be no tapping-thenthe copper-section must be uniform throughout and sufli'cient -to carry the I On theoth'er'ha nd, "if the number of turns is fixed -(i:-e.--tappings are not used) "the only possi 1 bility'of varying the amperage is to provide means for varying the reluctanceo'f the magnetic circiiit. It is well known, on suchbasis; to providea magnetic "core with relatively *movable parts; the

" movement I being so arrange-dfa's to*vary either the reluctance -of the magnetic" circuityfor the coupling between the copper and the iron. v I An open-ended solenoid with-relativelymovamen-en core and coil is an eiiample-f Variation ofcoupling onlyi butsuch an arrangement is very limited in its range ofcurrent variatiom though providing maximum efiiciency for the 1 higher Consequently, an open-ended solenoid' {becomes very large and expensive in -m'aterial and electrical losses Where large range of variation of iatively;

1 c5 Glaims. (emu-+119)- closed magnetic circuitwith'amovable part for *variation 'ofits reluctance; has I a-wider range of current variation -but for the same weight of =-copp'er:and iron it is" not possible to obtainthe 5 --same maximumamperage as with an open-ended -s'olenoid, because the inherent impedance is higher. Consequently, the efficiency is also lower for the higher amperages. But, such c0nstruc tion--has ahigher efliciencythan an open ended V '1 0 solenoid for the lower a'mperages.

Thebbjebt' or the present inventionis an improved construction 'ofivariable electro-magnetic l1 'device-suchias a choke, transformer 'or the like, :combining the advantages of' each ot the aforel5 said -basid forms of-open endedsolenoid'or closed I magnetic circuit.

-'-According tothe invention a variable electromagnetic device such as a choke, transformer or the' lilre comprising a-shell shaped magnetic '20 c'0re consisting of an outer frame and a central limb' acrossi the frame vvith' at least one electric windingon the corearranged so as to produce therein a: shell 'shaped magnetic flux, is characterised: in thatthe said central limband frame Bo -are relatively movable -so as to open or close the i magnetic circuit at least between one end of the a :limb andtheii'fram'e; whereby greater current and. :flux' v'ariation may be obtained 'for the same a'mou'nt ot copper and iron.

1 The expression shellshaped magnetic flux i is- -used herein to describe" that arrangement of magnetic flux ina shell -shaped': core in which athe flux in' the centre limb isin onedirection'and 'is the sum -of the flux fr'om'the two parts of the 5 frameoneabhsidebf the said centre limb. Pref ierably theflux in each off'the said two parts is Lsubstantially equalsothat-there is symmetry or "balance. r I

. theaccompanying drawings:

F ig.' 1 'is' a perspective diagram'showing one ex'ample of an electro magnetic choke made in iaccordance-withthezlinvention;

:"Figl z is a perspectivediagrammatic view show- :ing the-centre limb of the choke shown in Fig. 1 ;Eigimshows anzalternative construction of the mouter-iframe;

Fig. 3A shows an alternative:construetionof centrelimb o :'Fig.'i 4 ;shows flan: alternative' wiriding 6f the 50 mexamplei'shown; in Fig. .1

:Fi'g'. 5;..is :a'fdiagram' showing a modified construction for the frame;

sE'igs-ifi" and :7 :iarezfragmentary views "showing ;.'.furthenmiodifiedconstructions for one end of a 55o;vframe,;1- 1 l cross section.

Fig. 8 shows a construction with the parts tapered;

Fig. 9 is a fragmentary diagram showing pole shadowing for the centre limb;

Fig. 10 is a fragmentary view showing mechanical counter-balancing of the magnetic forces;

Fig. 11 shows a potentiometer made in accordance with the invention;

Fig. 12 shows a modification of the construction shown in Fig. 11 for use as a twin choke.

In the example of the invention shown in Figs. 1 and 2 a choke for 230 volts 10 amps. 50 cycles comprises a bottle-shaped outer frame consisting of 15 laminations (shown diagrammatically as 2 laminations) of standard gauge and usual material, divided longitudinally at b. to reduce eddy current losses and for that purpose made of two parallel sets of laminations a, 11 The overall inside dimensions of such frame are substantially 3% inches between the sides of th frame, which sides are 3 inches wide; From the base to the neck of the bottle the frame is about 6 inches and the neck is about 2 inches long. The parts forming the neck are therefore of such length that the area of the air gap between such parts and the centre limb is greater than the cross sectional area of the said centre limb as described below.

Slidably located in the neck of the bottle is a centre limb shown separately in Fig. 2, consisting of a group of about 80 to 90 laminations (shown diagrammatically as 12 laminations) collectively forming a core of about 1% inch square The laminations are divided from the bottom by a cut at c, and are secured together by a series of rivets din the centre of each limb thus formed. The cut at 0' reduces eddy and other currents which might otherwise be induced in circuits formed by the rivets and thus cause heating and losses. Such core, when the inner end is against a thin interposed insulator e at the base of the bottle-shaped frame projects at its other or outer end about /2 inch beyond the neck of the frame. This insulator provides the usual basic air gap and also prevents magnetic adhesion. A thin insulating guide tube 1 of rectangular cross section is'provided within the frame extending substantially from the base to the end of the neck constituting a former for the electric winding g and a guide for the sliding core 0 as well as providing something againstwhich the laminations of the frame at the neck may be clamped by a clamp h. The

upper end of thecentre limb laminations c are secured by a clamp c -and movement of the sliding centre limb may be effected by cam, lever, screw or other suitable mechanism connected to such clamp and either manually or power operated. The winding 9 occupies substantially the Whole of the space between the sides of the frame and the centre core.. The relatively long neck provides a sufficiently large area of air gap or gaps to reduce the reluctance at such position to compensate for the unavoidable thickness of the insulating tube 7. It also provide stability for the sliding tube and noiseless location for the sliding centre core or limb.

As shown in Fig. 3A, the laminations c of the centre limb are arranged in the plane at'right angles to those shown in Fig. 2 and this isfound to increase the efficiency and the laminations can be made a stampings.

In operation, as the centre limb c is withdrawn through the neck of the bottle-shaped frame the basic air gap between the inner end of the centre limb and the base of the bottle-shaped frame, as determined by the thickness of the interposed insulator e, is progressively increased and thereby quickly reduces the impedance of the apparatus. When the centre limb is fully in the device has all th characteristics of a choke having a shell-shaped core whilst when the centre limb is fully withdrawn so that its inner end is within the neck of the frame, the choke will have substantially the same characteristics as an openended solenoid without any iron core. Intermediate characteristics are provided by intermediate positions of the sliding centre limb and thus in one device it is possible to obtain the full range of variation hitherto obtainable only by the use of the two comparable separate types of chokes or relatively inefliciently by much larger chokes of either type. Instead of th winding being on the centre limb, a balanced pair or pairs of windings g are provided as shown in Fig. 4 on the sides of the frame, with the result that the flux of the two windings come into opposition progressively as the centre limb is withdrawn.

As shown diagrammatically in Fig. 5 the choke comprises an outer frame 1' formed with necks i and i one at each end between which is an insulating guide tube 2' in which is located a sliding centre limb i The choke is shown with a winding 1' around the insulating guide tube. The centre limb has an extension 2' of non-magnetic material secured thereto at the lower end as a guide member.

In operation, the provision of the neck at the lower end as well as at the upper end of the frame provides a better mechanical construction for guiding the centre limb and also enables one [to have a greater area at the air gap for the passage of the flux.

As shown in Fig. 6, the neck may be formed by inward bending at 7" of the laminations 7' of the frame or as shown in Fig. 7 some of the laminations of the frame It may be bent outwardly at k while others are bent inwardly at 10 at the other end shall be the main or a near as possible the only variable.

' Of course, the device may have a plurality of windings or tappings to provide additional characteristics and uses for example as an autotransformer. 7

As shown in Fig. 8, the frame m is tapered to have inclined sides and there is a correspondingly shaped winding m to provide modification of its characteristic. Thus, by providing a winding'which is wider at the base than at the neck, there will be an increase in the available range of variation as well as increase of the variation effect at the initial stages of movement of the centre limb m as its end approaches or recedes from the insulation m at the base of the frame. By reversing the taper, the available range of variation will still be increased but with reduction of the variation effect at the initial stages of movement.

As shown in Fig. 9, the inner end of the centre limb n may be pole shadowed in known manner by means of short-circuit rings n, n to reduce physical vibration. Alternatively a single short-circuit winding as shown dotted at n may be sunk in the laminations facing the end of shown in Fig. 10, in order to reduce the relatively high physical force required to produce initial outward movement of the centre limb from its in position, return springs 0 may be incorporated in the construction of the device as j compression springs between a clamp o for the laminations of the centre limb o and the uppershoulder of the frame 0 p The device made in accordance with the invention has characteristics particularly suitable for use as a dimmer or as a choke for a welding as shown in Fig. 6 adjacent and in alignment,

and with a common slidable centre limb 31 The two windings 10 p on the centre limb are in series with the load L across one of them. Displacement of the centre limb :0 will vary-the relative reluctance of the two coils and consequently alter the potential gradient.

As a further physical modification, the centre limb, instead of being axially slidable through the bottle neck of the frame it may be laterally movable in any desired manner, as by pivoting. Such an arrangement is shown in Fig. 12 as applied to the construction of Fig. 11 for providing a twin choke in which the frames p and p are connected by side members p and are pivoted at p to the centre limb so that they can be displaced angularly as shown, so that the impedance of each choke varies simultaneously and equally.

What I claim is:

1. A'variable electromagnetic device comprising a shell-shaped magnetic core having an outer frame, a central limb within said frame and at least one winding on said core to produce a shellshaped magnetic flux, said frame consisting of a plurality of laminations bent to provide substantially parallel fiat sides and defining a relatively wide space, the end portions of said sides being bent to form restricted neck portions, the

latter being substantially parallel, said frame' being slit in a plane transversely of said laminations, said central limb consisting of a plurality of laminations slidably fitting between said neck portions and extending into said space, the direction of movement of said limb being substantially parallel to said sides.

2. A variable electromagnetic device comprising a shell-shaped magnetic core having an outer frame, a central limb within said frame and at least one winding on said core to produce a shellshaped magnetic fiux, said frame consisting of a plurality of laminations bent to provide substantially parallel flat sides and defining a relatively wide space, the end portions of said sides being bent to form restricted neck portions, the latter being substantially parallel, said central limb consisting of a plurality of laminations slidably fitting between said neck portions and extending into said space, said limb being slit in a plane transversely of said laminations, the direction of movement of said limb being substantially parallel to said sides.

3. A variable electromagnetic device comprising a shell-shaped magnetic core having an outer frame, a central limb within said frame and at least one winding on said core to produce a shellshaped magnetic flux, said frame consisting of a plurality of laminations bent to provide substantially parallel fiat sides and defining a relatively wide space, the end portions of said sides being bent to form restricted neck portions, the latter being substantially parallel, said central limb consisting of a plurality of laminations slidably fitting between said neck portions and extending into said space, the direction of movement of said limb being substantially parallel to said sides, and an insulating tube within said frame, said limb being mounted Within said tube.

4. A variable electromagnetic device comprising a shell-shaped magnetic core having an outer frame, a central limb within said frame and at least one winding on said core to produce a shellshaped magnetic flux, said frame consisting of a plurality of laminations bent to provide substantially parallel fiat sides and defining a relatively wide space, the end portions of said sides being bent to form restricted neck portions, the latter being substantially parallel, said central limb consisting of a plurality of laminations slidably fitting between said neck portions and extending into said space, the direction of movement of said limb being substantially parallel to said sides, and an insulating tube within said frame, said limb being mounted within said tube, said neck portions being clamped to said tube.

5. A variable electromagnetic device compris ing a shell-shaped magnetic core having an outer frame, a central limb within said frame and at least one winding on said core to produce a shellshaped magnetic flux, said frame consisting of a plurality of laminations bent to provide substantially parallel fiat sides and defining a relatively wide space, the end portions of said sides being bent to form restricted neck portions, the latter being substantially parallel, said central limb consisting of a plurality of laminations slidably fitting between said neck portions and extending into said space, the direction of movement of said limb being substantially parallel to said sides, a second similar frame the neck portions thereof facing the neck portions of said first frame and in alinement therewith, said limb extending into and slidable in both of said frames.

HEINRICH MULLER.

REFERENCES CITED The following references are of record in the file of this patent:

. UNITED STATES PATENTS Number Name Date 1,098,549 Barnum June 2, 1914 1,684,746 Smith et al. Sept. 18, 1928 1,874,806 Ross Aug. 30, 1932 2,091,842 West Aug. 31, 1937 2,113,603 Polydoroif Apr. 12, 1938 2,447,002 Faust et a1. Aug. 17, 1948 

